Marine diesel engines of this type, in which the power turbine is used for generating the necessary shipboard electrical energy, are known.
Thus, for example, a generator can be directly coupled to the reduction gear of the high speed power turbine. A unit of this type has the advantage that it can be accommodated wherever space is freely available in the ship's engine room, with the condition that the gas ducts should not be too long. The disadvantage of this solution is the requirement for expensive power electronics to control the turbine/generator unit to a specified rotational speed. Electronic controls of this type cost a multiple of the turbine and price causes them to be excluded from the short list of possibilities for overcoming the above disadvantage. The obvious employment of economical asynchronous generators is also excluded because, in contrast to stationary installations where the electrical grid (which is generally large) keeps the turbine/generator unit at constant rotational speed, the total shipboard power in the case of marine installations is approximately of the same order of magnitude as that of the power turbine. The shipboard grid is, therefore, incapable of keeping the rotational speed of a power turbine/asynchronous generator unit constant.
Another possible speed control system, in which a synchronous generator is coupled to the power turbine and this unit is controlled by means of butterfly valves located in the exhaust gas, cannot be used either. The factors paeticularly opposing the use of this arrangement are the expensive arrangement of controllable butterfly valves in the exhaust gas flow of installations fired with heavy oil and the difficulty of calculating dynamic processes in the long exhaust gas ducts.
Another way of employing the power turbine for generating electricity is possible in the case of marine diesel engines which themselves drive a speed-controlled generator. In this case, the power turbine can be coupled to the free end of the shaft of the generator. Because of the expensive speed control, however, a large number of marine engines are not equipped with their own generator. Generally speaking, provision is made for the output of the power turbine to be supplied to the crankshaft of the main engine via a gear, which is also an expensive solution.
The object of the invention is therefore to use the power turbine for at least partially covering the electricity requirements of a marine installation of the type discussed above and to do this in a simple, economical and reliable manner.
According to the invention, this is achieved by the power turine being coupled to a free shaft end of the auxiliary diesel/generator unit.
The advantages of this arrangement are clear. All the additional generators, gears and controls mentioned above can be avoided. Without any change to the concept and without design effort, existing installations can be retrofitted or converted in the shortest possible time with the new arrangement. On this point, it should be mentioned that, at the time the invention of the present application was made, power turbines associated with supercharged marine diesel engines are not yet in operation and that, therefore, the abovementioned known solutions together with their shortcomings are of a theoretical nature.